Which of these would you consider: 1) more playable, 2) has better modulation capabilities, and 3) as better for sequencing into deep hypnotic tracks?

They're within $100 of each other so price isn't really a consideration so much as sound and tweaking. I'm thinking the winner will be sequenced with a Doepfer Dark Time or an Elektron Analog Four.

I've been getting rid of some synths lately, so don't want to buy something I'll wind up selling again. For example: DSI Mono Evolver Keyboard - didn't care for the oscillators or filters (to me sounded cheap and rude) and the blue lights were giving me a headache. Moog Lil' Phatty - very musical, but no matter how much I turned the knobs couldn't get the range of sound I was after.

I think if you're going to get an Analog 4 to sequence it with anyway then get that first and see what you feel like you need afterward. On paper the MS is more playable (keyboard) and has more mod options (bigger patchbay, 2 oscs). The only thing that I think a DE mkI has going for it over the MS is the MS seems closer in tone to the A4 than the DE so you might want the DE for variety. But apart from that I'd be looking at the MS in your situation, and definitely the A4 over the Dark Time.

neither are better than the other...there are very different sounds and apps for each, along with the obvious aesthetic and form-factor differences

ms-20 is more of a studio army-knife. a bit like an 'arp2600 jr' without the reverb, adds a resonant hipass, and lacks just a few other bitsDE is a synth expander sort of unit, albeit not at all lacking in modulation and usefulness, either. DE+DT of course works straight away and are made for each other, while MS-20 runs Hz/V so it's limited choices there ---or you kludge a voltage converter in between the MS and whatever v/Oct sequencer you prefer.

Mod section + p locks + patch change per step (which gives you essentially another complete mod matrix to work with on each step). I don't know of any other analogue synth that can do that.

You're including the features of the digital sequencer and fx sections, along with the specific paths of how they're implemented here, in your definition of 'analogue synth'. Any system with a scanner onboard can change to another patch per note/gate/step. naturally that could get expensive, so the A4s 'flexible but mostly closed' architecture is an ideal compromise, for those that are inclined to that sort of thing.

if you'd said 'beats any groovebox' i can agree... for the money, anyway. It is such an extremely affordable ready-solution to a formerly (very) expensive proposition. AHhhhh the things we can do with cheap memory and clever coding+hardware design.